Preventative Monitoring and how it can minimize your Solar O&M expenses – Part II

The number of solar PV installations in the United States and Europe that are maturing into post-warranty stage assets are becoming a problem for many solar system owners and asset managers. The need for reliable solar operations and maintenance (O&M) becomes even more critical as an important contributor to investment return. PV solar plants are investments that are likely to last for 20–25 years or more, and that’s why in order to arrive at an accurate ROI figure, smart O&M planning can take you a long way.

Solar providers risk losing warranties from the Original Equipment Manufacturers (OEMs) if their O&M service fails to properly maintain the systems according to warranty requirements. It is important to have the right O&M strategy and know what is actionable and non-actionable when addressing underperformance.

The power output delivered from a photovoltaic module depends heavily on the amount of irradiance reaching the solar cell. Even a small amount of soiling can have a noticeable impact on generation so it’s not hard to imagine how much energy is lost in some situations such as snowfall. Soiling on a few panels can cause noticeable underperformance on certain strings which will reduce the amount of DC electricity flowing into the inverter. However, in the event of snowfall, where snow can completely cover the surface of a large portion of the array, it is possible that no energy will be produced at all.

How can we identify one type of shading underperformance from the other and what can we do about it?

In the case of snowfall, the absolute easiest way to verify that the underperformance is caused by snow is by looking at the environmental kit. If you’re ambient temperature is below freezing, your panel temperatures will likely be even colder if they have a layer of snow or ice sitting on top. You should always check the local weather reports for your asset but generally if these two parameters are below freezing it will be your strongest indicator. For most solar projects, the best way to handle snowfall is just to let it melt in the sun. It doesn’t make any sense to pay for snow removal if it will melt within a day or two.

String level underperformance as covered in “part I” is more difficult to notice and has a much smaller effect on real-time plant generation. The key detail here is that the long term damage to the array can also be much more severe in this case. Bird droppings and dirt patches that cover small sections of a panel, act as a resistance to current generated from the other clean cells. This causes the shaded cell to heat up and leads to hot spotting that can eventually damage the module. The resistance to current also effects the voltage output of each string feeding the inverter. This makes it difficult for the inverter to seek the optimum voltage level, at which, the maximum power is delivered. For these types of shading, it is important to identify the cause and address it (Ex. bird nesting or wind-blown debris). If this sounds like something you see regularly on your array, panel washing should be an integral part of your O&M contract if you want to maximize your output.

Trackers:

Trackers help generate more electricity due to the increase in direct exposure to sunlight. This increase can be as much as 10 to 25% depending on the geographic location. Underperformance issues related to trackers are relatively easy to spot and depending on how your data looks you can even tell what direction your trackers are facing when they break. When looking at solar performance, the standard bell curve is a best case scenario, where generation increases in the morning, plateaus in the afternoon and dies down again in the evening. If you don’t have tracker monitoring available, comparing the daily generation trends on your inverters will help you identify when repairs are needed. There are three basic data trends you should keep an eye out for when monitoring for underperformances related to tracker alignment:

Late inverter start-up (morning) – Modules may be stuck facing West

Early production decline (Evening) – Modules may be stuck facing East

Underperformance on the shoulders of the bell curve and possibly a dip in peak hour production depending on the time of year (afternoon) – Modules may be stuck at rest position (facing directly up)

Overheating:

This is a very common cause for underperformance in inverters, especially during the summer months. Like all electronic equipment, Inverters generally operate best at cooler temperatures and have to utilize sensors, fans and heat sinks to regulate their internal temperatures. Poor heat dissipation is usually caused by dust, fan issues and air duct blockage. Sometimes, the air temperatures are just too high that the inverter has to de-rate itself to a lower power output just to keep running, and is likely to return to normal operations once it cools down. In this case underperformance is usually limited to the hottest hours of the day and the shoulders of the bell curve should look relatively normal. Most inverters will start to de-rate at around 40° – 45° Celsius (104° – 113° F) so it is important to verify with your environmental kit when you notice this production trend as it might not need a technician to investigate immediately. A broken component like a fan may cause extended underperformance throughout the day and is likely to reoccur every day until a repair is made. Your inverter will try to generate in the morning when the temperature is cool and then crash soon afterwards as heat is generated converting DC to AC. This can happen even at normal or low ambient temperatures and is definitely a cause for dispatch.

About Arbox:

Arbox Hap® allows you to track all the O&M activities in your portfolio. Contact an Arbox representative today and see a demo of how you can automate aspects of you project monitoring, KPI’s and alarm notifications.

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